Multiedge lapping

ABSTRACT

Apparatus is disclosed for simultaneously lapping spaced parallel faces on a workpiece by means of an elongate lapping tool which has a plurality of spaced lapping faces. The lapping faces may be formed as a helical surface on the lapping tool so that rotation of the lapping tool results in the faces on the workpiece being lapped by a number of separate portions of the helical surface and results in the workpiece being moved along the lapping tool so that each face is lapped successively by a number of different portions of the helix.

United-States Patent 1191 Walker et al. Sept. 3, 1974 [5 MULTIEDGE LAPPING 3,708,925 1/1973 Ainoura 51 /206 P [75] Inventors: Peter Albert Walker, Stevenage; FOREIGN PATENTS QR APPLICATIONS @1 11; g ';g5 of 392,385 .4 1933 Great Britain 51/26 England Primary Exammer-Al Lawrence Smith [73] Assignee: International Computers Limited, Assistant E i Ni h l P, G dici London, England Attorney, Agent, or FirmMisegades, Douglas & Levy 22 Filed: Dec. 11, 1972 21 Appl, No.: 309,843 [571 ABSTRACT Apparatus is disclosed for simultaneously lapping [30] Foreign Application Priority Data spaced parallel faces on a workpiece by means of an D l 1971 Great Britain 55733 [71 elongate lappmg tool which has a plurahty of spaced lapping faces. The lapping faces may be formed as a I helical surface on the lapping tool so that rotation of 5i" f 51/ the lapping tool results in the faces on the workpiece u on being a num er of sep e po t o f e [58] Fleld of 51/206 g helical surface and results in the workpiece being moved along the lapping tool so that each face is lapped successively by a number of different portions [56] References Cited of the helix UNITED STATES PATENTS 3,429,305 2/1969 Hall 125/11 R 6 Clam, 6 Drawmg Flgul'es 3 2 a) l I \\l 1 I p -p-i 1 \v\ l MULTIEDGE LAPPING BACKGROUND OF THE INVENTION This invention relates to lapping a plurality of edges of a workpiece.

In the manufacture of assemblies of magnetic transducing heads for simultaneous co-operation with a plurality of tracks of a recording medium, it is necessary that the relative positioning of the poles of the different heads in the assembly should be both accurate and consistent as between different assemblies so that multi. track records produced by one head assembly can be read back by means of another head assembly. In addition the width of each head must be equal in order to ensure that the width of the recording does not change with change of head as this would result in variation in the strength of the signal read out from the record.

SUMMARY OF THE INVENTION According to the invention apparatus for lapping a plurality of spaced parallel faces on a workpiece to produce finished parallel faces at a predetermined spacing includes a lapping tool having lapping faces spaced apart by a distance related to said predetermined spacing; means to cause first relative movement between the lapping faces and the workpiece to effect lappingof said parallel faces and means to cause second relative movement between the lapping tool and the workpiece such that each of said faces is lapped successively by a plurality of said lapping faces.

BRIEF DESCRIPTION OF THE DRAWING Embodiments of the invention will now be described, by way of example, with referenceto the accompanying drawing, in which:

FIG. 1 shows a side view of a ferrite comb member to be lapped to form a plurality of accurately located and dimensioned head portions.

FIGS. 2A and 2B are useful in describing how bevels are lapped on the combmember to form defmed magnetic head surfaces. r

FIG. 3 shows diagrammatically, an elevation of one arrangement for performing the lapping :operations of FIGS. 2A and 2B.

FIG. 4 is a section on the line X--X of FIG. 3.

FIG. 5 is a section similar to that of FIG. 4 showing an alternative arrangement for holding and guiding the ferrite comb member during lapping.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows a comb structure of ferrite material having a base 11 from which six projections 12 extend, each projection being centred approximately on equally spaced portions 13. The projections 12 may be separate members fixed to, rather than integral with, a base which then need not be of the same material as the projections. The comb structure may'be utilised for the formation of the cores of a group of magnetic transducing heads in which case each of the projections 12 will be formed into a core of a magnetic head, and a nonmagnetic gap will extend through each projection 12 parallel to the plane of the drawing. Such gaps may be provided by mounting two ferrite blocks together with a small space therebetween and filling the space with glass which then serves to bond the blocks together.

' jections so as to leave the end faces of the projections having accurate dimensions and extending equally on either side of the portions 13 to the dotted lines 14, 14'. The material may be removed so as to leave the end portions of the projections with substantially parallel sides or the projections may be bevelled on each side so that the width of the end faces of the projections is defined by intersections of the bevelled faces with the end faces.

The material is removed from the projections 12 by means of a lapping operation using an elongate lapping tool which has a plurality of parallel lapping faces spaced apart by a distance equal to the spacing of the portions 13. The number of lapping faces of the lapping tool is greater than the number of projections 12. In

order to perform the lapping operation, the lapping tool is moved relative to the projections whilst maintaining one edge of each projection 12 in contact with a different one of the lapping faces respectively. In order to ensure that the spacing between adjacent projections is as accurate as possible, the comb structure is repeatedly moved lengthwise of the lapping tool so that each of the projections are lapped by a succession of lapping faces. Thus if there is any inaccuracy in the spacing of the lapping faces, which would have resulted in the projections being lapped inaccurately, the spacing of the lapped sides of the projections will be related to the average accuracy of spacing of the lapping faces rather than the absolute accuracy of spacing of particular lapping faces.

A particularly convenient form of lapping tool for effecting this lapping operation consists of a threaded lead screw. FIG. 2A shows part of such a lead screw 20 suitable for bevelling the sides of the projections 12 of the ferrite comb 10. The pitch of the thread is equal to the desired spacing of the portions 13 and the angle of the helical side walls 21, 24 of the thread is equal to the angle of bevel which it is desired to form on the projections. When the lead screw 20 is rotated about its axis and the comb 10 is held against rotation and is maintained with the projections 12 bearing against the side wall 21, the lead screw 20 acts as a lapping tool with the side wall of each turn of the lead screw 20 acting as a lapping face to remove the dashed parts 22 of each projection 12 and thereby produce the bevels 23.

FIG. 2B shows the same elements as FIG. 2A but with I the other side of the projections 12 maintained bearing against the other side wall 24 of the thread of the lead screw 20. Suitable rotation of the lead screw 20 then results in removal of the parts 25 to produce the bevels 26.

Lapping of the bevels 23 and 26 is continued for as long as is necessary for the resulting flat faces 27 between the bevels 23, 26 on the projections 12 to corresponding to the spacing 14 to 14' of FIG. 1.

FIGS. 3 and 4 show the lapping lead screw 20 rotatably mounted in end frames 31, 32. The ferrite comb 10 is secured by any convenient means to a slide block 33 which is able to slide along and pivot about a rod 34 extending parallel to the lead screw 20. The block 33 pivots under the action of gravity so that the projections 12 enter the spaces between the turns of the thread of the lead screw 20 but is prevented from pivoting to such an extent that the projections bear against both side walls of the thread simultaneously by means of a pad 35 bearing against a stop in the form of a rod 36 extending parallel to the lead screw 20. The lead screw 20 is rotatably driven selectively in forward and reverse directions from a shaft 37 via a transmission unit 38(Rotation of the lapping lead screw 20 in a forward direction causes one wall of the thread to bear against one edge of the projections 12 and, while lapping one side of the projections 12, moves the ferrite comb and block 33 along the rod 34. When the block 33 approaches one end of the rod 34, the direction of rotation of lapping lead screw is reversed which causes the other wall of the thread to bear against the projections 12 and, while lapping the other side of the projections 12, moves the ferrite comb 10 and block 33 along the rod 34 in the opposite direction. The lapping lead screw is driven alternately in forward and reverse directions to lap the two sides of the projections 12 alternatively until the desired dimensions on the end faces of the projections 13 have been attained. The position of the stop' rod 36 may be adjusted (by means not shown) in the end frames 31, 32 to permit adjustment of the position of the projections 12 relative to the lapping screw 20.

FIG. 5 shows an alternative construction of sliding holder for the ferrite comb 10. The comb 10 is held beor otherwise to' facilitate loading the vice with a ferrite comb. Additionally or alternatively, a mechanism, such as a lever arrangement, may be provided for retracting the vice against its spring loading.

The projections 12 or other members to be lapped need not be spaced to be lapped by adjacent turns of the thread. Further, they need not be equally spaced provided that they are spaced by multiples of the pitch of the thread so that they contact the same side wall and so have corresponding bevels.

We claim:

1. Apparatus for the simultaneous lapping of a plurality of side-by-side regions on a workpiece to produce lapped faces at a predetermined spacing including; an elongate lapping tool member having a longitudinal axis; a workpiece support means;

a first helical surface defining along the tool member a plurality of side-by-side first lapping faces spaced apart by said predetermined spacing; mounting means for rotatably supporting the tool member for rotation about its longitudinal axis; guide means for the workpiece support means extending lengthwise of the tool member for enabling the workpiece support means to traverse lengthwise of the tool member; and

a supporting connection between the workpiece support means and the guide means enabling, when a workpiece is mounted in the support means, a readily releasable simultaneous engagement with said first lapping faces of the faces to be lapped along the full length thereof and a controlled continuous loading of the workpiece towards the tool -member thereby to maintain throughout said lapping a predetermined continuous lapping pressure between the workpiece and the tool member.

2. Apparatus as claimed in claim 1, in which the rotation of the tool member causes the workpiece to traverse lengthwise of the tool member thereby to move each of the faces to be lapped successively into engagement with successive ones of the first lapping faces.

3. Apparatus as claimed in claim 1, in which the elongate tool is provided with a second helical surface defining along the tool member a plurality of side-by-side lapping faces operable to lap further side-by-side faces on the workpiece, said further faces alternating with the first mentioned faces of the workpiece.

4. Apparatus as claimed in claim 3, in which rotation of the lapping tool in a first direction is effective to cause lapping engagement between the first helical surface and the workpiece first faces, and rotation of the lapping tool in a second direction opposite to the first direction is effective to cause lapping disengagement of the first helical surface from the workpiece and lapping engagement of the second helical surface with the workpiece second faces.

5. Apparatus as claimed in claim ,1, in which the workpiece support means is pivotally mounted on the guide means and pivots under the action of gravity towards the lapping tool, said apparatus including stop means for limiting the extent to which the workpiece faces can approach the tool member. I

6. Apparatus as claimed in claim 1, in which the workpiece support means includes;

a slide member slidably engaged with the guide means, a connection clamp for receiving the workpiece and adapted for slidable coupling to the slide member for movement of the workpiece towards and away from the tool member; and resilient means for biassing the connection clamp towards the tool member. 

1. Apparatus for the simultaneous lapping of a plurality of side-by-side regions on a workpiece to produce lapped faces at a predetermined spacing including; an elongate lapping tool member having a longitudinal axis; a workpiece support means; a first helical surface defining along the tool member a plurality of side-by-side first lapping faces spaced apart by said predetermined spacing; mounting means for rotatably supporting the tool member for rotation about its longitudinal axis; guide means for the workpiece support means extending lengthwise of the tool member for enabling the workpiece support means to traverse lengthwise of the tool member; and a supporting connection between the workpiece support means and the guide means enabling, when a workpiece is mounted in the support means, a readily releasable simultaneous engagement with said first lapping faces of the faces to be lapped along the full length thereof and a controlled continuous loading of the workpiece towards the tool member thereby to maintain throughout said lapping a predetermined continuous lapping pressure between the workpiece and the tool member.
 2. Apparatus as claimed in claim 1, in which the rotation of the tool member causes the workpiece to traverse lengthwise of the tool member thereby to move each of the faces to be lapped successively into engagement with successive ones of the first lapping faces.
 3. Apparatus as claimed in claim 1, in which the elongate tool is provided with a second helical surface defining along the tool member a plurality of side-by-side lapping faces operable to lap further side-by-side faces on the workpiece, said further faces alternating with the first mentioned faces of the workpiece.
 4. Apparatus as claimed in claim 3, in which rotation of the lapping tool in a first dirEction is effective to cause lapping engagement between the first helical surface and the workpiece first faces, and rotation of the lapping tool in a second direction opposite to the first direction is effective to cause lapping disengagement of the first helical surface from the workpiece and lapping engagement of the second helical surface with the workpiece second faces.
 5. Apparatus as claimed in claim 1, in which the workpiece support means is pivotally mounted on the guide means and pivots under the action of gravity towards the lapping tool, said apparatus including stop means for limiting the extent to which the workpiece faces can approach the tool member.
 6. Apparatus as claimed in claim 1, in which the workpiece support means includes; a slide member slidably engaged with the guide means, a connection clamp for receiving the workpiece and adapted for slidable coupling to the slide member for movement of the workpiece towards and away from the tool member; and resilient means for biassing the connection clamp towards the tool member. 